Generally, basic phenates have a remarkable effect of neutralizing or dispersing acids such as oxy acids and sulfuric acid or sludge, lacquer and carbon to thereby prevent corrosion wear, ring groove clogging and piston ring sticking from occurring when such substances are used or found in lubricating oils for internal combustion engines.
In so far as typical conventional methods for introducing sulfur into phenates are concerned, two methods are generally known. One of them is a method wherein an alkylphenol is treated with sulfur chloride to form a sulfide which is then converted into a metal salt. The other is a method wherein sulfurization is carried out by using elemental sulfur during metal addition or after previously forming a metal salt (phenate). The present invention belongs to the latter sulfurization method.
Many past attempts have been made to produce over-based phenates by using the latter sulfurization method. For example, U.S. Pat. No. 2,680,096 discloses a method for producing basic sulfurized calcium phenate wherein starting materials comprising phenols, calcium base, sulfur and a dihydric alcohol are heated to carry out a sulfurization-metal addition reaction. Furthermore, over-based phenates containing alkaline earth metals in an amount of at least twice the theoretical amount of hydroxyl group of phenols have been obtained by a one-step reaction in recent years. For example, Hori and Hayashida (Japanese Patent 1,303,226) had found out that highly basic alkaline earth metal phenates can be unexpectedly produced by carrying out sulfurization and a metal addition reaction simultaneously in the presence of an excess of phenols and the treating the resulting product with carbon dioxide. Further, Hori, Ueda et al (JP-A-59-31724 (the term "JP-A" as used herein means an "unexamined published Japanese patent application")) had found out that when the above-mentioned reaction is carried out by adding water to the reaction system, the metal addition reaction proceeds smoothly, and the conversion of alkaline earth metal reagents into products can be kept at a high level and the distillation time and associated utility costs of production of the reaction products after the metal addition reaction can be greatly reduced even when the amount of the dihydric alcohol to be used is reduced.
However, the alkaline earth metal contents of the products obtained by these methods are at most 300% of theoretical amount. Further, there are disadvantages that when the alkaline earth metal contents of the products are increased, performance as lubricating oil additive or fuel oil additive is lowered, and, particularly, oil solubility and stability are lowered when these conventional products are added to engine oil.
The present inventors have conducted studies to solve these problems as associated with the prior art as mentioned above. The present inventors have found that when the metal addition reaction and sulfurization are carried out simultaneously under pressure and closed conditions that highly over-based alkaline earth metal phenates can be produced in comparison with the instance where metal addition and sulfurization are carried out under atmospheric or super-atmospheric pressure and open condition. Specifically, these unexpected results are observed in the reaction for carrying out simultaneously the metal addition to phenols and the sulfurization of the phenols by adding an alkaline earth metal reagent and sulfur to a phenol and reacting them as carried out under pressure and closed conditions.
Further, the present inventors have unexpectedly found that remarkably high-based alkaline earth metal phenates can be produced by carrying out metal addition under pressure and closed conditions and carrying out sulfurization and carbon dioxide treatment under pressure without deaeration in the reaction. This process comprises adding an alkaline earth metal reagent to a phenol, reacting them to carry out metal addition to the phenol and then adding sulfur thereto to simultaneously carry out sulfurization and carbon dioxide treatment. The present invention has been accomplished on the basis of these findings.
Water and hydrogen sulfide are formed with the progress of the reaction in the metal addition--sulfurization reaction by using the phenols, the dihydric alcohol elemental sulfur and the alkaline earth metal reagent. As described above, Hori and Ueda et al (JP-A-59-31724) have found that when said reaction is carried out by adding water to the reaction system, the metal addition reaction proceeds smoothly, the conversion of the alkaline earth metal reagents into the products can be kept at a high level and the distillation time and utility costs of the reaction products after the metal addition reaction can be greatly reduced even when the amount of the dihydric alcohol to be used is reduced and that these effects cannot be attained only by the presence of water formed in the course of the reaction.
According to conventional wisdom, it was considered proper and desirable to remove or vent hydrogen sulfide formed during the reaction out of the reaction vessel; i.e., use an open condition. Accordingly, the reaction of metal addition to the phenols by reacting phenols with alkaline earth metal reagents or the reaction for carrying out simultaneously the metal addition and sulfurization by reacting the phenols, the alkaline earth metal reagents and sulfur, has been conventionally carried out under atmospheric or super-atmospheric pressure and open conditions. Though the exact mechanism with which the sulfurization and metal addition reaction proceeds is not specifically understood beyond what is known as to the chemical structure of the product, it is an unexpected finding by the present inventors that when hydrogen sulfide or water formed during the reaction is confined within the reaction system i.e., use a closed condition that remarkably high-based alkaline earth metal phenates can be produced in comparison with the instance where said reaction is carried out under atmospheric or super-atmospheric pressure and open conditions. The resulting products of the present invention have excellent performance as a lubricating oil additive or a fuel oil additive and are particularly excellent in oil solubility and stability when added to engine oil.